(1) Field of the Invention
The present invention relates to an injection control apparatus for a diesel engine.
(2) Description of Related Art
In a common rail system (CRS) diesel engine for general purpose use including an industrial use, an agricultural use, and the like, a microprocessor unit (MPU) for exerting main control and a driver for driving hardware are provided within an engine control unit (ECU). A driver for driving an injector plays an important role in control of an engine, and is called an “injector driver”. An MPU is an injection control apparatus which calculates an injection timing and an injection time, and provides an instruction signal indicating a suitable injection timing and a suitable injection time to a so-called injector driver described above.
Generally, a current is fed to an injector driver in two stages of a stage in which a current of a first hold is fed and a stage in which a current of a second hold is fed. For a current of a first hold, a large current is required in order to open a core valve. On the other hand, a current of a second hold may be a current smaller than the current of the first hold because the current of the second hold has only to maintain the opened core valve. Accordingly, an apparatus is known which is configured to achieve reasonable injection using the above-described two-stage injection in which a strong current is firstly fed and thereafter a weak current is fed.
Conventionally, in an injection control apparatus, a time of a first hold of a driving current for the injector described above is generally set to a predetermined time having an optimum value. However, even though an MPU is arranged so as to control driving of the injector with a time of a first hold being set to an optimum value, an actual injection amount may probably vary by various factors such as a temperature condition.
Therefore, it is impossible to follow a change in an environmental condition or the like by only providing an apparatus which sets a time of a first hold to an optimum value in design phase. This may result in an increase or a decrease of an actual amount of injection from the injector with respect to an indicated amount of injection, and thus, such an apparatus still has room for improvement as the injection control apparatus.